Booster

[1] A radio device which amplifies the signal or the audio output to the speakers. Because of its size it is mounted in the glovebox, under the dash, in the center console, under the seat, or in the trunk.
[2] A device incorporated in vehicle system (such as brakes and steering), to increase the pressure output or decrease amount of effort required to operate, or both.
[3] A common term applied to the case of a compressor when used as the first stage in the cascade refrigerating system.
[4] A rocket engine, or cluster of engines, forming part of a launch system, either the first stage or auxiliary stage, used to provide an initial thrust greater than the total lift-off weight. Also called booster rocket.
See also battery booster, brake booster, hydraulic brake booster, power booster, spring booster, vacuum booster, vacuum brake booster